This invention relates to a helium compressor, and particularly to a helium compressor provided with an attached cooling system which can efficiently cool down a compressor and a driving motor installed in a casing.
In a helium compressor apparatus using helium gas as a refrigerant gas, generally, a large heat is generated from the compressor in its operation and the compressor is put in a state of high temperature, because the adiabatic coefficient of the helium gas is as great as K=1.66. In addition, the motor driving this compressor is also put in a state of high temperature with its driving rotation, and thus a state of considerably high temperature is caused in a hermetically-sealed casing.
To cope with this state, a cooling system as shown in FIG. 2 is usually employed.
In FIG. 2, a compressor 2 and a motor 3 driving this compressor 2 are disposed in a hermetically-sealed casing 1, and a low-pressure gas inside the hermetically-sealed casing 1 is sucked in and compressed by the compressor 2, and then it is discharged as a high-pressure gas outside the casing 1 through a discharge port 4. The discharged high-pressure gas passes through an expansion unit 5 and thereafter it is collected again into the hermetically-sealed casing 1 through a suction port 6.
In order to cool down the compressor 2 and the motor 3 disposed in hermetically-sealed casing 1, a cooling pipe 7 is wound around and along the outer periphery of the casing 1, and cooling water is made to circulate through pipe 7 by a mechanical pump or the like (not shown), so as to cool down the hermetically-sealed casing 1 itself, and thus the compressor 2 and the motor 3 are cooled down.
However, this kind of cooling system is so designed as to cool down the outer periphery of the hermetically-sealed casing 1 and further to cool down the compressor 2 and the motor 2 by utilizing the heat transfer effect of the gas inside the casing 1, and therefore it suffers problems, as pointed out heretofore, that a satisfactory cooling efficiency can not always be attained, and consequently, the life of the motor 3 is shortened.